The present invention relates to an electronic component with which a package is formed by molding a solid electrolytic capacitor or a semiconductor chip, with lead wires led out from the package. More particularly, the invention relates to an electronic component having improved soldering performance and adhesion properties of the lead wires when they are soldered to the circuit substrate or the like.
Electronic component, e.g., a tantalum capacitor, is made by first electrically connecting a capacitor element 21 formed of a sintered body of e.g. tantalum powder provided with various treatments such as chemical conversion coating, with electrical connection of the anode and cathode to the lead frame 22 as shown in FIG. 8(a), then resin molding a capacitor element part into a package 23 as shown in FIG. 8(b). In the exemplified case, a cathode is connected with the lead wire through a fuse 26. And, as the illustrative view of the section of the product is shown in FIG. 8(c), each lead is separated from the lead frame 22 and the leads 24, 25 are bent along the package 23 to manufacture an electronic component. And, it is, for example, placed on the pattern coated with a solder paste of the circuit substrate and then heated to be assembled into the circuit substrate.
In order to make the soldering performance favorable in soldering to the circuit substrate, the lead frame material is plated on its whole surface with, for example, a 91 solder (Sn:Pb=9:1) before being assembled.
However, when the solder as mentioned above is used, due to its high melting point, solder wettability is not sufficiently secured in mounting, and defective of mounting may result. On the other hand, it may be conceived to use a solder having low melting point, e.g., a 64 solder (Sn:Pb=6:4) as a material for solder plating, but when a 64 solder is used, the solder tends to fuse in molding for forming a package 23 or in mounting, causing a gap A between the leads 24, 25 and the package 23 [ref. FIG. 8(c)] to be formed, thereby providing a tendency for entry of water or the like and a problem of lowering of reliability.
As described above, in case of solder plating under the lead frame state, when a solder having a high melting point is used, no sufficient solder wettability can be secured for the lead frame in mounting into the circuit substrate or the like. Furthermore, when a solder having a low melting point is plated under the lead frame state, the solder is fused in the next molding or packaging to cause a gap to be formed between the lead and the package, leading to the problem of lowering of moisture resistance. To cope with this, there has been adopted a method of plating with a solder having low melting point only on the lead part which is exposed from the package after the molding, but it requires much increased number of work steps and provides a cause for hike in cost.
In addition, accompanied with the tendency of constriction in size of the electronic parts, the lead width becomes extremely fine to no more than about 1 mm, and the adhesion area by soldering becomes very small, so that there may be problems that the fixation capacity becomes insufficient when the wettability of the solder is not favorable even in a small extent, thus showing a tendency for the electronic parts to be disengaged under effect of vibration or external force, as shown in FIG. 9. In FIG. 9, the part 20 is a solid electrolytic capacitor, 31 is a substrate to be mounted such as circuit substrate, and 32 is a cream solder.
The present invention has been made to solve the problems as above, and its object is to provide an electronic component with which soldering performance can be improved in mounting by a simple work without causing a problem of moisture resistance between the lead and the package, and without requiring the work of number of steps of solder plating on the exposed leads after molding.
Another object of the present invention is to provide an electronic component of the structure that can improve fixation of the solder after mounting.
The electronic component according to the present invention comprises an electronic component chip, leads whose one end parts are electrically connected with the electrodes of the electronic component chip, and a package which covers the electronic component chip and the one end parts of the leads, wherein the other end parts of the leads are extended outside from the package, and bent along the outer wall of the package, and a solder bump of low melting point is held in the gap between the leads and the package.
By adopting this structure, when, for soldering the electronic component to a circuit substrate or the like, the electronic component is placed on the circuit substrate coated with a solder cream and the temperature is elevated, firstly a low melting point solder held between the leads and the package is fused to spread over the whole leads to provide good wettability, and then the cream solder is fused to run, thus running well to the whole leads, so that the soldering performance is improved.
If the above solder bump is stored in the recess provided in the package, sufficient amount of solder material can be retained. The recess can be formed either on the surface (back surface) of the side to be soldered on the circuit substrate or on the side wall. Alternatively, the solder bump may be fixed to the leads and stored in the recess, or fixed to the inside of the recess for storage.
If the through hole provided on the other end parts of the leads, the solder material goes into the through hole to cause increase in the adhesion area, thereby making it possible for the solder material to adhere to the other end parts of the leads in a clamping manner, thus providing great improvement to the fixation force.
Furthermore, due to the bending of the leads in a manner to make the other end parts thereof the soldered face and the through hole being continuously formed from the soldered face to the opposite side with respect to the bent portion, the applied solder is more easily filled up above the level of the soldered face, which is desirable.
The provision such that a part of the solder bump is to be accommodated in the through hole is desirable because the solder is made to run more easily to both the surface and the reverse face of the lead and to improve wettability.
The electronic component is formed of, for example, a solid electrolytic capacitor.
Another aspect of the electronic component of the present invention comprises an electronic component chip, leads for electrically connecting at its one end parts with electrodes of the electronic component chip and a package for covering the electronic component chip and the one end parts of the leads, wherein the other end parts of the leads are extended outside from the package, a through hole is provided on the other end parts, and a low melting point solder bump is retained in the through hole.